Hello all! I am making a Laser MIDI Controller for my Senior Design project, and would like some advice from the community on what to do about proximity detection. What I would like to do is add a Thermin effect to the MIDI sound. I will attempt to explain the playing area to give you some idea of the space the user will be playing in.

Imagine a desktop-style lecturn, with the surface one would normally set his books or notes on being the control surface. Milled into this surface is a cavity approximately 1 inch deep. From the top of the cavity, a series of 12 laser diodes are radiating a series of 12 photodetectors located at the bottom of the cavity (currently, we are experimenting with photodiodes, but have plans to test phototransisitors to see which one gives better (more stable) performance). The dimensions of the cavity are as follows: approximately 14" wide x approximately 9" tall x approximately 1" deep. The user plays the controller by placing his fingers within the cavity and in the paths of the laser beams. You break a beam, you play a note.

I'm sure you've seen these types of things before (Laser Harps), but as you may have guessed, how one interacts with the lasers can have an impact on how you execute some features...

Our thought was to use a proximity detector to sense when we slide our finger up and down the laser's path. Sliding the finger up would cause the pitch to bend up and sliding the finger down would cause the pitch to bend down. So, with that in mind, here's what I've done for the last two weeks:

I've been looking at IR proximity sensors, light-to-frequency components, and ultrasound sensors and I'm having a hard time figuring out which one would be ideal for this application. Most of the IR proximity sensors look really promising after reading the datasheets, but a Google search on those of you who have used them on the Arduino report the "real" results and sensitivities, and they turn out to be not-so-ideal...so, I think I've researched so much that I can't make a decision at all.

Any input you have would be extremely helpful and very much appreciated.

I guess until it gets moved, I could ask you about this: I am using PD438C/S46 photodiodes. I did wire up one of them and irradiated it with a laser pointer and it does turn on/off LEDs as the beam is interrupted.

Is it possible (do you think) to get this sensor to do double duty by turning off the MIDI note when the laser is present and turning on the MIDI Note AND reading the "proximity" of the finger to bend the note appropriately?